* {
     box-sizing: border-box;
     margin: 0;
}

/******************************************
/* BASE STYLES
/*******************************************/
html {
     font-size: 62.5%;
     font-family: sans-serif;
}
.category_list {
     display: inline;
}
h2 {
     font-size: 3em;
     text-align: center;
}
.exercise_container {
     width: 50%;
     border: 0.25em solid lightseagreen;
     border-radius: 1em;
     margin: 2%;
     height: 50vh;
}
li {
     list-style: none;
     padding: 2%;
}
a {
     text-decoration: none;
}

/******************************************
/* LAYOUT
/*******************************************/
body {
     height: 100vh;
     display: flex;
     justify-content: center;
     align-items: center;
}
#category_list {
     display: flex;
     justify-content: center;
     align-items: center;
}
.exercise_container {
     display: flex;
     justify-content: center;
     align-items: center;
}
.exercise_info {
     text-align: center;
}
footer {
     position: absolute;
     bottom: 0;
     padding: 1%;
}
/******************************************
/* ADDITIONAL STYLES
/*******************************************/
/* Small Screen, Laptop */
@media all and (min-width: 1251px) {
     .exercise_container {
          width: 25%;
     }
}
/* iPad, Tablet */
@media all and (max-width: 1250px) and (min-width: 481px) {
     #category_list {
          display: block;
          text-align: center;
          padding-top: 5%;
     }
}
/* Mobile */
@media all and (max-width: 480px) {
     body {
          flex-direction: column;
     }
     .exercise_container {
          width: 90%;
     }
}