* {
      box-sizing: border-box;
    }

    body {
      margin: 0;
      min-height: 100vh;
      display: grid;
      place-items: center;
      background: #f7f7f7;
      font-family: Arial, Helvetica, sans-serif;
      color: #111;
    }

    .math-card {
      width: min(860px, 96vw);
      min-height: 680px;
      padding: 64px 16px 48px 58px;
      display: grid;
      grid-template-columns: minmax(280px, 1fr) 380px;
      column-gap: 54px;
      align-items: start;
      background: #fff;
      border: 1px solid #e5e5e5;
      border-radius: 0 0 18px 0;
      box-shadow: 0 1px 2px rgba(0, 0, 0, 0.12);
    }

    .problem {
      width: 100%;
      max-width: 260px;
      padding-top: 0;
      justify-self: center;
      font-size: 112px;
      font-weight: 400;
      line-height: 1.05;
      text-align: right;
    }

    .number1 {
      min-height: 118px;
      padding-right: 0;
      text-align: right;
    }

    .second-row {
      display: flex;
      align-items: center;
      justify-content: flex-end;
      gap: 18px;
      padding-right: 0;
    }

    .operator {
      font-size: 100px;
      line-height: 1;
      font-weight: 300;
    }

    .number2 {
      width: 112px;
      min-width: 112px;
      text-align: right;
    }

    .underline {
      height: 13px;
      width: 100%;
      margin-top: 12px;
      background: #222;
    }
	.answer {
	  height: 1.2em;
	  min-height: 1.2em;
	  display: flex;
	  align-items: center;
	  justify-content: flex-end;
	  white-space: nowrap;
	  font-variant-numeric: tabular-nums;
	}
    .keypad {
      display: grid;
      grid-template-columns: repeat(3, 1fr);
      gap: 15px 16px;
      width: 100%;
      margin-top: 0;
    }

    .key {
      min-width: 0;
      height: 117px;
      display: grid;
      place-items: center;
      padding: 0;
      border: 2px solid #c9c9c9;
      border-radius: 17px;
      background: #fff;
      box-shadow: 0 2px 3px rgba(0, 0, 0, 0.18);
      color: #111;
      font: inherit;
      font-size: 96px;
      font-weight: 600;
      line-height: 1;
      cursor: pointer;
      transition: background 120ms ease, transform 120ms ease;
	  outline: none;
    }

    .key:hover {
      background: #f4f4f4;
    }

    .key:active {
      transform: translateY(1px);
      box-shadow: 0 1px 2px rgba(0, 0, 0, 0.16);
    }

    .zero {
      grid-column: 1 / span 2;
    }
	  .back-link {
	  position: fixed;
	  top: 15px;
	  left: 15px;
	  padding: 12px 20px;
	  background-color: #4f46e5;
	  color: white;
	  text-decoration: none;
	  font-size: 20px;
	  font-weight: bold;
	  border-radius: 10px;
	  box-shadow: 0 4px 0 #312e81;
	  transition: background-color 0.2s, transform 0.2s;
	  z-index: 1000;
	}

	.back-link:hover {
	  background-color: #4338ca;
	  transform: translateY(-2px);
	}

	.back-link:active {
	  transform: translateY(2px);
	  box-shadow: 0 2px 0 #312e81;
	}
    @media (max-width: 700px) {
      .math-card {
        min-height: auto;
        padding: 28px 18px;
        grid-template-columns: 1fr;
        row-gap: 32px;
      }

      .problem {
        max-width: 240px;
        font-size: 84px;
      }

      .number {
        min-height: 88px;
      }

      .operator {
        font-size: 76px;
      }

      .keypad {
        max-width: 380px;
        justify-self: center;
        gap: 10px;
      }

      .key {
        height: clamp(68px, 18vw, 100px);
        font-size: clamp(52px, 12vw, 78px);
        border-radius: 13px;
      }
}